.\" $Id: curl_multi_socket.3,v 1.7 2006-08-01 08:57:32 bagder Exp $
.\"
.TH curl_multi_socket 3 "9 Jul 2006" "libcurl 7.16.0" "libcurl Manual"
.SH NAME
curl_multi_socket \- reads/writes available data
.SH SYNOPSIS
#include <curl/curl.h>

CURLMcode curl_multi_socket(CURLM * multi_handle, curl_socket_t sockfd,
                            int *running_handles);

CURLMcode curl_multi_socket_all(CURLM *multi_handle,
                                int *running_handles);
.SH DESCRIPTION
Alternative versions of \fIcurl_multi_perform(3)\fP that allows the
application to pass in one of the file descriptors/sockets that have been
detected to have \&"action" on them and let libcurl perform. This allows
libcurl to not have to scan through all possible file descriptors to check for
action. When the application has detected action on a socket handled by
libcurl, it should call \fIcurl_multi_socket(3)\fP with the \fBsockfd\fP
argument set to the socket with the action.

At return, the int \fBrunning_handles\fP points to will contain the number of
still running easy handles within the multi handle. When this number reaches
zero, all transfers are complete/done. Note that when you call
\fIcurl_multi_socket(3)\fP on a specific socket and the counter decreases by
one, it DOES NOT necessarily mean that this exact socket/transfer is the one
that completed. Use \fIcurl_multi_info_read(3)\fP to figure out which easy
handle that completed.

The curl_multi_socket functions inform the application about updates in the
socket (file descriptor) status by doing none, one or multiple calls to the
socket callback function set with the CURLMOPT_SOCKETFUNCTION option to
\fIcurl_multi_setopt(3)\fP. They update the status with changes since the
previous time this function was called.

To force libcurl to (re-)check all its internal sockets and transfers instead
of just a single one, you call \fBcurl_multi_socket_all(3)\fP. This is
typically done as the first function call before the application has any
knowledge about what sockets libcurl uses.

Applications should call \fBcurl_multi_timeout(3)\fP to figure out how long to
wait for socket actions \- at most \- before doing the timeout action: call
the \fBcurl_multi_socket(3)\fP function with the \fBsockfd\fP argument set to
CURL_SOCKET_TIMEOUT.

.SH "CALLBACK DETAILS"

The socket \fBcallback\fP function uses a prototype like this
.nf

  int curl_socket_callback(CURL *easy,      /* easy handle */
                           curl_socket_t s, /* socket */
                           int action,      /* see values below */
                           void *userp,    /* private callback pointer */
                           void *socketp); /* private socket pointer */

.fi
The callback MUST return 0.

The \fIeasy\fP argument is a pointer to the easy handle that deals with this
particular socket. Note that a single handle may work with several sockets
simultaneously.

The \fIs\fP argument is the actual socket value as you use it within your
system.

The \fIaction\fP argument to the callback has one of five values:
.RS
.IP "CURL_POLL_NONE (0)"
register, not interested in readiness (yet)
.IP "CURL_POLL_IN (1)"
register, interested in read readiness
.IP "CURL_POLL_OUT (2)"
register, interested in write readiness
.IP "CURL_POLL_INOUT (3)"
register, interested in both read and write readiness
.IP "CURL_POLL_REMOVE (4)"
deregister
.RE

The \fIsocketp\fP argument is a private pointer you have previously set with
\fIcurl_multi_assign(3)\fP to be associated with the \fIs\fP socket. If no
pointer has been set, socketp will be NULL. This argument is of course a
service to applications that want to keep certain data or structs that are
strictly associated to the given socket.

The \fIuserp\fP argument is a private pointer you have previously set with
\fIcurl_multi_setopt(3)\fP and the CURLMOPT_SOCKETDATA option.
.SH "RETURN VALUE"
CURLMcode type, general libcurl multi interface error code.

If you receive \fICURLM_CALL_MULTI_PERFORM\fP, this basically means that you
should call \fIcurl_multi_perform\fP again, before you wait for more actions
on libcurl's sockets. You don't have to do it immediately, but the return code
means that libcurl may have more data available to return or that there may be
more data to send off before it is "satisfied".

NOTE that this only returns errors etc regarding the whole multi stack. There
might still have occurred problems on individual transfers even when this
function returns OK.
.SH "TYPICAL USAGE"
1. Create a multi handle

2. Set the socket callback with CURLMOPT_SOCKETFUNCTION

3. Add easy handles

4. Call curl_multi_socket_all() first once

5. Setup a "collection" of sockets to supervise when your socket
callback is called.

6. Use curl_multi_timeout() to figure out how long to wait for action

7. Wait for action on any of libcurl's sockets

8, When action happens, call curl_multi_socket() for the socket(s) that got
action.

9. Go back to step 6.
.SH AVAILABILITY
This function was added in libcurl 7.15.4, although not deemed stable yet.
.SH "SEE ALSO"
.BR curl_multi_cleanup "(3), " curl_multi_init "(3), "
.BR curl_multi_fdset "(3), " curl_multi_info_read "(3)"
